1990 SC wont start

sam jones

Registered User
Good afternoon

Did you check the following?

Battery voltage prior to start.

Check coil pack connector for security/corrosion.

Check for spark. See youtube scannerdanner attachment.

Engine harness ground on the back of the driver side cylinder head for corrosion or security.


Add fuel system cleaner.

Fuel pressure regulator/vacuum line. Check vacuum line for security, evidence of fuel leakage/smell.



Did you check fuel pressure holding pressure with gauge. Does it bleed off immediately?


Might have stuck open/close fuel injectors. This is a known issue when a car has not run for long periods of time. When you changed the spark plugs was there any evidence of fuel?

Check signal from EEC to accessible fuel injector connectors with a Noid test light (should be able to rent at a discount auto parts store) or remove the supercharger to get access to all injectors.



Do they pulse during start attempt? If so EEC is not the issue.



Here are some food for thought searches that might help.


 

Hiram1

Registered User
i do have the same issue before you have kicked me out of this team. Thanks i have explained you before Doug H. but you did not listen to me brother. sorry fo an advanced. this is my same issue. I had it for over 7 months now. i have fix all the harness and still getting codes 121.542. replaced ECM, IRCM. cranks and cranks never fires, the engine never starts. when i got it start the engine will do the same way. foot all way to the floor and it went like when the car has no gas and goes off. now it doesnt event do that. im wondering if its the start engine. have read in the internet this :
Electrical connections fail.
Magnetic switch (start relay) defective or slow.
The electric motor has an electrical fault.
Pinion gear system with damaged freewheel, pinion or freewheel.
 

decipha

Registered User
I had a friends 89 supercoupe have the exact same issues as the OP, except it happened in minutes. Car drove perfect and everything was fine. Parked in front the house and went back out to fire her up 10 minutes later and same issues. It took me about 10 minutes of tinkering to find it was a vac leak. It was one of the vac lines on the back of the plenum had came loose.
 

Mranalla07

Registered User
You stated that the vac/boost gauge bounces when running? I'm wondering if a intake valve or valves are stuck open?
That would kind of coincide with it ran fine before it was put into storage, & now it has this issue. Just a thought though.
I know on a naturally aspirated engine that a bouncing vac gauge usually indicates that, but not sure with the supercharger.

Anyone else have any thoughts or know?
MOST of these older cars with boost gauges in the dash are not accurate. They are electronic read outs not mechanical. When compared to a mechanical gauge you can tell. I bet the boost gauge was bouncing around due to the rough idle and the different system voltage provided by the alternator due to the rough idle. Naturally aspirated cars and supercharged/turbocharged cars will have same or similar vacuum readings at idle. Neither is working at idle so engine vacuum is not affected. Your altitude it the world (BARO) and the camshaft specs of the engine are what make your engine vacuum what it is at idle. If the car ran fine before you stored it and now it does not run it could be 2 things. Bad gas or rodents got to some wiring. assuming nothing else was touched.
 

BrianD1978

Registered User
I had a chance to work on the car again last few days. I put a code reader on and was getting only a code 23 (TPS out of range) and code 24 (Air charge sensor out of range) I decided to clean the ground behind the drivers headlight and check for spark. I Hooked the spark tester to #1 and the car started for the 1st time in over a year. I ran ok but with a idle that would ramp up and down on its own like a vacuum leak. I checked the fuel pressure while running and had 40 psi with my new pressure regulator that I put on. I pulled out of the garage and started the car on and off few the next few hours with only the idle issue. I pulled back in the garage and let it sit over night. New morning I tried to start it and had the same no start issue as before. I replaced the tps and the charge air sensor. Checked for spark and have spark on all wires. Now cranking I have a check red engine light. Hooked up my cheap code reader and now can't get that to work. I pretty sure I have some goofy electrical issue or a bad plug even though they a new. I'll pull the plugs when I get some help pushing the car up on ramps. This thing is such a a pain to figure out. Any thoughts or ideas welcome. Thanks
 

KMT

Registered User
I put a code reader on and was getting only a code 23 (TPS out of range) and code 24 (Air charge sensor out of range)

New morning I tried to start it and had the same no start issue as before. I replaced the tps and the charge air sensor. Checked for spark and have spark on all wires. Now cranking I have a check red engine light. Hooked up my cheap code reader and now can't get that to work.
Odd that both would go out, more likely yet another ground issue, and/or 5v supply voltage, which I believe they both share. That voltage should be between 4.3v & 5.0v. Might be a corrosion issue in the upstream harness...ask me how I know. Be sure that battery voltage is near 12.4v

Check the ground cable from the pass. side motor mount over to the body. Replace if crusty. See this no-start checklist if you haven't already: https://mnharms.com/tutorials/disnostart/ - be sure to confirm good ground from DIS rear bolts to battery. Know how to do voltage drop tests?
 

35th

Registered User
My understanding is that the red check gauge light has to do with them cam sensor so if it doesn't start first try... If you unplug cam sensor (careful to not allow plug to snag in serpentine belt) and try to start it it should eventually start... So with sensor unplug the computer has to guess at when to fire the number 1 so it can take serval tries but it should start if your having some sort of issue along those lines I'd say eoth cam sensor or possibly a bad/correded wire to dis harness....
 
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